Install macOS helper from PKG for XPC enroll

Browser enrollment used osascript on every elevate. Ship a signed
privileged helper installed at PKG time so probo:// can enroll over
XPC with no second admin prompt. Add make install/uninstall/clean for
local PKG test loops, and show alerts only on failure.

Mirror the Go lint path for the macOS SPM package: Make
targets, root configs, and a Linux CI job. Keep checks
syntax-only so they do not need a macOS SDK. Format the
existing sources so the new gates start clean.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

cmd/probo-agent/installer/macos/enroll-ui/Shared/HelperProtocol.swift

@@ -0,0 +1,13 @@
+import Foundation
+
+@objc(ProboAgentHelperProtocol)
+public protocol ProboAgentHelperProtocol: NSObjectProtocol {
+    func getVersion(withReply reply: @escaping (String) -> Void)
+    func ping(withReply reply: @escaping (Bool) -> Void)
+    func install(
+        serverURL: String,
+        enrollmentToken: String,
+        configDir: String,
+        withReply reply: @escaping (Int32, String?) -> Void
+    )
+}